Liquid crystal display device

ABSTRACT

A liquid crystal display device includes a liquid crystal layer which is arranged between first and second aligning films formed on inner sides of first and second substrates, has liquid crystal molecules twist-aligned in a direction from the first aligning film toward the second aligning film when an electric field is not applied between first and second electrodes, and generates retardation of substantially λ/2 with respect to transmitted light. First and second polarizing plates are arranged on outer sides of the first and second substrates. A transmission axis or an absorption axis of the first polarizing plate is substantially matched with a direction along which the liquid crystal molecules in the vicinity of the first aligning film are aligned when a sufficiently intensive electric field is applied.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation Application of U.S. application Ser. No.11/369,155, filed Mar. 6, 2006, which is based upon and claims thebenefit of priority from prior Japanese Patent Application No.2005-064970, filed Mar. 9, 2005, the entire contents of both of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device havinga liquid crystal layer in which liquid crystal molecules aretwist-aligned at an angle of substantially 90°.

2. Description of the Related Art

There has been conventionally known a twisted nematic type liquidcrystal display device in which liquid crystal molecules in a liquidcrystal layer held between a pair of substrates are twist-aligned fromone substrate toward the other substrate. As disclosed in Jpn. Pat.Appln. KOKAI Publication No. 88962-1994, in a TN type liquid crystaldisplay device in which liquid crystal molecules are twist-aligned at anangle of approximately 90°, each polarizing plate is set on a front sidewhich is an observation side of display of a liquid crystal cellincluding a twisted nematic liquid crystal layer and on a rear sidewhich is an opposite side of the front side.

An optical axis of one of a transmission axis and an absorption axis ofeach of the pair of polarizing plates is positioned in a directionparallel with or perpendicular to a direction of aligning treatmentapplied to an aligning film of each substrate of the liquid crystalcell, and optical axes of the respective polarizing plates are arrangedto be parallel with or perpendicular to each other. In the liquidcrystal display device in which the optical axes of the respectivepolarizing plates are arranged in parallel with each other, dark displayin which transmission of light is substantially prevented (normallyblack display) is obtained in a state where an electric field is notsubstantially applied to the liquid crystal layer (a normally state).Further, in the liquid crystal display device in which the optical axesof the respective polarizing plates are arranged to be perpendicular toeach other, bright display in which light transmission becomes maximum(normally white display) is obtained in the normally state.

In the normally white display, in order to obtain dark display, asufficiently intensive electric field is applied to the liquid crystallayer to rise the liquid crystal molecules in a direction vertical tothe substrates, and the twisted alignment state is released, therebyobtaining dark display.

However, in the normally white display, since the liquid crystalmolecules are strongly affected by an alignment restricting force by thealigning treatment applied to the aligning films in the vicinity of eachaligning film provided on an inner surface of each substrate which is incontact with the liquid crystal to restrict alignment of the liquidcrystal molecules, a so-called “anchoring effect” by which behaviors ofthe liquid crystal molecules are suppressed provokes a reduction incontrast at the time of application of the electric field mentionedabove (at the time of on) or tone reversal in an intermediate tone,thereby resulting in a decrease in display quality.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a liquid crystaldisplay device which can obtain normally white display with a goodquality which has sufficiently high contrast and has no tone reversal inan intermediate tone.

According to a first aspect of the present invention, there is provideda liquid crystal display device comprising:

a first substrate having at least one first electrode on one side;

a second substrate which is arranged to face said one side of the firstsubstrate, and has at least one second electrode facing the firstelectrode on one side facing the first substrate;

a first aligning film which is provided on said one side of the firstsubstrate, and subjected to aligning treatment in a first direction;

a second aligning film which is provided on said one side of the secondsubstrate, and subjected to aligning treatment in a second directioncrossing the first direction at a predetermined angle;

a liquid crystal layer which is arranged between the first aligning filmand the second aligning film, has liquid crystal molecules twist-alignedin a predetermined direction from the first aligning film toward thesecond aligning film when an electric field is not applied between thefirst and second electrodes, and generates retardation of substantiallyλ/2 with respect to transmitted light;

a first polarizing plate which is arranged on an opposite side of thefirst substrate, and arranged in such a manner that an optical axis ofone of a transmission axis and an absorption axis is substantiallymatched with a third direction along which the liquid crystal moleculesin the vicinity of the first aligning film are aligned when asufficiently intensive electric field is applied between the first andsecond electrodes; and

a second polarizing plate which is arranged on an opposite side of thesecond substrate, and arranged in such a manner that an optical axis ofone of a transmission axis and an absorption axis is set to besubstantially perpendicular to the optical axis of the first polarizingplate.

According to a second aspect of the present invention, there is provideda liquid crystal display device comprising:

a first substrate having at least one first electrode on one side;

a second substrate which is arranged to face the one side of the firstsubstrate, and has at least one second electrode facing the firstelectrode on an opposite side of the first substrate;

a first aligning film which is arranged on the one side of the firstsubstrate, and subjected to aligning treatment in a first directioninclined at substantially 45° with respect to a horizontal line in alateral direction as seen from an observation side;

a second aligning film which is arranged on the one side of the secondsubstrate, and subjected to aligning treatment in a second directioncrossing the first direction at substantially 90°;

a liquid crystal layer which is arranged between the first aligning filmand the second aligning film, has liquid crystal molecules twist-alignedat substantially 90° from the first aligning film toward the secondaligning film when an electric field is not applied between the firstand second electrodes, and generates retardation of substantially λ/2with respect to transmitted light;

a pair of viewing angle compensating films formed of discotic liquidcrystal layers which are respectively arranged between the firstpolarizing plate and the first substrate and between the secondpolarizing plate and the second substrate in such a manner that theirrespective optical axes are set in substantially parallel withdirections of aligning treatment processing applied to the aligningfilms of the respective adjacent substrates;

a first polarizing plate which is arranged on an opposite side of thefirst substrate in such a manner that an optical axis of one of atransmission axis and an absorption axis is substantially matched with athird direction along which the liquid crystal molecules in the vicinityof the first aligning film are arranged when a sufficiently intensiveelectric field is applied between the first and second electrodes; and

a second polarizing plate which is arranged on an opposite side of thesecond substrate in such a manner that an optical axis of one of atransmission axis and an absorption axis becomes substantiallyperpendicular to the optical axis of the first polarizing plate.

Furthermore, according to a third aspect of the present invention, thereis provided a liquid crystal display device comprising:

a first substrate having at least one first electrode formed on oneside;

a second substrate which is arranged to face the one side of the firstsubstrate, and has at least one second electrode facing the firstelectrode on one side facing the first substrate;

a first aligning film which is arranged on the one side of the firstsubstrate, and subjected to aligning treatment in a first directioninclined at substantially 45° with respect to a horizontal line in alateral direction as seen from an observation side;

a second aligning film which is arranged on the one side of the secondsubstrate, and subjected to aligning treatment in a second directioncrossing the first direction at substantially 90°;

a liquid crystal layer which is arranged between the first aligning filmand the second aligning film, has liquid crystal molecules twist-alignedat substantially 90° in a predetermined direction from the firstaligning film toward the second aligning film when an electric field isnot applied between the first and second electrodes, and generatesretardation which is substantially λ/2 with respect to transmittedlight;

a pair of viewing angle compensating films formed of discotic liquidcrystal layers which are respectively arranged between the firstpolarizing plate and the first substrate and between the secondpolarizing plate and the second substrate in such a manner that theirrespective optical axes become parallel with directions of aligningtreatment processing applied to the aligning films of the respectiveadjacent substrates;

a pair of retardation plates which are respectively arranged between thefirst polarizing plate and the viewing angle compensating film adjacentthereto and between the second polarizing plate and the viewing anglecompensating film adjacent thereto in such a manner that an optical axisof one of a phase advancing axis and a phase delaying axis becomessubstantially parallel with a direction of the optical axis of each ofthe adjacent viewing angle compensating films;

a first polarizing plate which is arranged on an opposite side of thefirst substrate in such a manner that an optical axis of one of atransmission axis and an absorption axis substantially matches with athird direction along which the liquid crystal molecules in the vicinityof the first aligning film are aligned when a sufficiently intensiveelectric field is applied between the first and second electrodes; and

a second polarizing plate which is arranged on an opposite side of thesecond substrate in such a manner that an optical axis of one of atransmission axis and an absorption axis becomes substantiallyperpendicular to the optical axis of the first polarizing plate.

According to the liquid crystal display device of the present invention,at the time of on where a sufficiently high electric field is applied tothe liquid crystal layer, an optical axis of a polarizing plate set onan outer surface of the substrate having an aligning film providedthereon is matched with a third direction in which liquid crystalmolecules in the vicinity of the aligning film are arranged. Therefore,linear polarized light which enters the liquid crystal layer at the timeof on is transmitted through the liquid crystal layer without beingaffected by birefringence based on an arrangement of the liquid crystalmolecules in the vicinity of the aligning film, and assuredly absorbedby the other polarizing plate arranged to be perpendicular to an opticalaxis on an opposed substrate side. As a result, sufficiently darkdisplay can be obtained, and hence normally white display with a goodquality which has high contrast and no none reversal in an intermediatetone can be stably acquired.

In the liquid crystal display device according to the first aspect ofthe present invention, it is preferable to arrange the first polarizingplate in such a manner that an optical axis of the first polarizingplate matches with a third direction which is a direction of anintermediate angle in a twist angle range in which the liquid crystalmolecules in the liquid crystal layer are twist-aligned from the firstaligning film toward the second aligning film. That is, the firstpolarizing plate is arranged in such a manner that its optical axismatches with the third direction rotated from an aligning treatmentdirection of one of the first and second aligning films toward thealigning treatment direction of the other one at an angle which issubstantially ½ of an angle formed between the aligning treatmentdirection of the first aligning film and the aligning treatmentdirection of the second aligning film. Moreover, it is preferable thatthe second aligning film is subjected to aligning treatment in a seconddirection crossing a first direction which is the aligning treatmentdirection of the first aligning film at substantially 90°, and that theliquid crystal molecules in the liquid crystal layer are twist-alignedat an angle of 90° from the first aligning film toward the secondaligning film. Additionally, it is desirable that each of the first andsecond substrates is constituted of a rectangular substrate having upperand lower sides extending in a lateral direction and right and leftsides extending in a vertical direction as seen from an observationside, each of the first and second aligning films is subjected toaligning treatment in a direction of 45° with respect to a horizontalaxis parallel with the upper and lower sides of the rectangularsubstrate, the first polarizing plate is arranged in such a manner thatits transmission axis faces a direction perpendicular to the horizontalaxis, and the second polarizing plate is arranged in such a manner thatits transmission axis is parallel with the horizontal axis. In thiscase, assuming that Δn is a refractive index anisotropy of the liquidcrystal layer with respect to transmitted light and d is a layerthickness of the liquid crystal layer through which the light istransmitted, it is preferable to set a product Δn·d of these values tofall within a range of 380 nm to 480 nm. Additionally, it is desirablethat color filters having a plurality of colors which selectivelytransmit different wavelength lights therethrough are arranged inaccordance with each pixel portion facing each electrode of the firstand second substrates, and a liquid crystal layer thickness is set todifferent values in accordance with the respective pixel portionscorresponding to the color filters having different colors. As a result,there can be obtained a liquid crystal display device with a highdisplay quality which assuredly prevents tone reversal in anintermediate tone from occurring with higher contrast.

Further, it is preferable to provide a configuration further including apair of viewing angle compensating films formed of discotic liquidcrystal layers arranged between the first polarizing plate and the firstsubstrate and between the second polarizing plate and the secondsubstrate in such a manner that their respective optical axes becomeparallel with the third direction and opposite to each other. As aresult, high contrast can be obtained, an effect of suppressing tonereversal in an intermediate tone can be acquired, and a viewing anglerestricting effect which avoids peek can be procured.

Furthermore, in the liquid crystal display device according to thepresent invention, it is preferable to further include a pair of viewingangle compensating films formed of discotic liquid crystal layersarranged between the first polarizing plate and the first substrate andbetween the second polarizing plate and the second substrate in such amanner that their respective optical axes become substantially parallelwith directions of aligning treatment processing applied to the aligningfilms of respective adjacent substrates. In this case, it is preferablethat a product Δn·d of a refractive index anisotropy Δn of the liquidcrystal layer with respect to light transmitted therethrough and a layerthickness d falls within a range of 450 nm to 550 nm. As a result, highcontrast and an effect of suppressing tone reversal in an intermediatetone can be obtained, and a wide viewing angle can be acquired.

Moreover, it is preferable to provide a configuration further includinga pair of retardation plates arranged between the first polarizing plateand the viewing angle compensating film adjacent thereto and between thesecond polarizing plate and the viewing angle compensating film adjacentthereto in such a manner that an optical axis of one of a phaseadvancing axis and a phase delaying axis becomes substantially parallelwith a direction of the optical axis of each adjacent viewing anglecompensating film. In this case, assuming that Δn is a refractive indexanisotropy of the liquid crystal layer and d is a layer thickness of theliquid crystal layer through which the light is transmitted, it isdesirable that a product Δn·d of these values is set to fall within arange of 350 nm to 450 nm and that retardation Re of the pair ofretardation plates is set to fall within a range of 15 nm to 55 nm.Additionally, it is desirable that each of the first and secondsubstrates is formed of a rectangular substrate and each of the firstand second aligning films is subjected to aligning treatment in adirection of substantially 45° with respect to one side of therectangular substrate. As a result, desired high contrast and an effectof suppressing tone reversal in an intermediate tone can be obtained,and an excellent display quality with a wide viewing angle can beacquired.

Further, like the liquid crystal display device according to the secondaspect of the present invention, in case of the liquid crystal displaydevice including the discotic liquid crystal layers arranged between thefirst polarizing plate and the first substrate and between the secondpolarizing plate and the second substrate in such a manner that theiroptical axes become substantially parallel with the direction of thealigning treatment processing applied to each of the aligning films ofthe respective adjacent substrates, it is preferable to arrange thefirst polarizing plate in such a manner that its optical axis matcheswith a third direction rotated from the aligning treatment direction ofone of the first and second aligning films toward the aligning treatmentdirection of the other one at an angle which is substantially ½ of anangle formed between the aligning treatment direction of the firstaligning film and the aligning treatment direction of the secondaligning film. Furthermore, assuming that Δn is a refractive indexanisotropy of the liquid crystal layer with respect to light transmittedtherethrough and d is a layer thickness of the liquid crystal layerthrough which the light is transmitted, it is desirable to set a productΔn·d of these values to fall within a range of 450 nm to 550 nm.Moreover, it is desirable that each of the first and second substratesis formed of a rectangular substrate having upper and lower sidesextending in a lateral direction and right and left sides extending in avertical direction as seen from an observation side, and that each ofthe first and second aligning films is subjected to aligning treatmentin a direction of substantially 45° with respect to a horizontal axisparallel with the upper and lower sides of the rectangular substrate. Asa result, desired high contrast and an effect of suppressing tonereversal in an intermediate tone can be obtained, and a very excellentdisplay quality with a wider viewing angle can be acquired.

Additionally, like the liquid crystal display device according to thethird aspect of the present invention, in a liquid crystal displaydevice including: a pair of viewing angle compensating films formed ofdiscotic liquid crystal layers arranged between the first polarizingplate and the first substrate and between the second polarizing plateand the second substrate in such a manner that their respective opticalaxes become substantially parallel with directions of the aligningtreatment processing applied to the aligning films of the respectiveadjacent substrates; and a pair of retardation plates arranged betweenthe first polarizing plate and the viewing angle compensating filmadjacent thereto and between the second polarizing plate and the viewingangle compensating film adjacent thereto in such a manner that anoptical axis of one of a phase advancing axis and a phase delaying axisbecomes substantially parallel with a direction of an optical axis ofeach adjacent viewing angle compensating film, it is desirable that eachof the first and second substrates is formed of a rectangular substrateand aligning treatment is applied to each of the first and secondaligning films in a direction of substantially 45° with respect to oneside of the rectangular substrate. Assuming that Δn is a refractiveindex anisotropy of the liquid crystal layer and d is a layer thicknessof the liquid crystal layer through which the light is transmitted, itis desirable to set a product Δn·d of these values to fall within arange of 350 nm to 450 nm and set retardation Re of the pair ofretardation plates to 15 nm to 55 nm.

Further, it is preferable that color filters having a plurality ofcolors through which different wavelength lights are selectivelytransmitted are respectively arranged in accordance with each pixelportion facing each electrode of the first and second substrates, and aliquid crystal layer thickness is set to different values in accordancewith the respective pixel portions corresponding to the color filtershaving the different colors. As a result, desired high contract, aneffect of suppressing tone reversal in an intermediate tone and viewingangle characteristics can be obtained, and an excellent color displayquality superior in color reproducibility can be acquired.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is an exploded plan view showing a liquid crystal display deviceas a first embodiment of the present invention;

FIG. 2 is a partially enlarged schematic cross-sectional view showing aninternal configuration of the liquid crystal display device;

FIGS. 3A and 3B are views illustrating an alignment state of liquidcrystal molecules at the time of off where an electric field is notapplied in the liquid crystal display device, in which FIG. 3A is a planview and FIG. 3B is a cross-sectional view;

FIGS. 4A and 4B are views illustrating an alignment state of liquidcrystal molecules at the time of on where an electric field is appliedin the liquid crystal display device, in which FIG. 4A is a plan viewand FIG. 4B is a cross-sectional view;

FIG. 5 is a graph showing change characteristics of a transmissionfactor with respect to an applied voltage in accordance with eachwavelength light in the liquid crystal display device;

FIG. 6 is an exploded plan view showing a liquid crystal display deviceas a second embodiment of the present invention;

FIG. 7 is a partially enlarged schematic cross-sectional view showing aninternal configuration of the liquid crystal display device;

FIG. 8 is a graph showing viewing angle characteristics in a lateraldirection in the liquid crystal display device according to the secondembodiment;

FIG. 9 is an exploded plan view showing a liquid crystal display deviceas a third embodiment of the present invention;

FIG. 10 is a graph showing viewing angle characteristics in a lateraldirection in the liquid crystal display device according to the thirdembodiment;

FIG. 11 is an exploded plan view showing a liquid crystal display deviceas a fourth embodiment of the present invention;

FIG. 12 is a graph showing viewing angle characteristics in a lateraldirection in the liquid crystal display device according to the fourthembodiment; and

FIG. 13 is an exploded plan view showing a conventional liquid crystaldisplay device.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

FIG. 1 is an exploded plan view showing an optical configuration of aliquid crystal display device as a first embodiment of the presentinvention, and FIG. 2 is a schematic cross-sectional view showing aninternal configuration of this element in an enlarging manner.

A liquid crystal display device according to this embodiment is anactive matrix type liquid crystal display device, and constituted of aliquid crystal cell 1 having a rectangular plane outer shape which hasfirst sides 1 a parallel with a horizontal axis 1 h in a lateraldirection of the liquid crystal display device and second sides parallelwith a vertical direction perpendicular to this horizontal axis 1 h asseen from an observation side. The display elements 1 includesrectangular front and rear polarizing plates 2 and 3 which arerespectively set on a front side as the observation side of display anda rear side with the liquid crystal cell 1 therebetween as shown in FIG.1.

In the liquid crystal cell 1, as shown in FIG. 2, a pair of front andrear glass substrates 11 and 12 are joined while maintaining apredetermined gap therebetween by a frame-shaped sealing material (notshown). A black mask 13 having an opening 13 a corresponding to eachpixel region is set on an opposed surface (an inner surface) of thefront glass substrate 11 which is one of the pair of joined glasssubstrates 11 and 12. In the black mask 13, the plurality of openings 13a corresponding to respective pixels are formed in a matrix arrangement.

Three types of color filters 14R, 14G and 14B of red, green and blue arerespectively set on a surface of the front glass substrate 11 facing therear glass substrate 12 in a predetermined arrangement in accordancewith each of the respective openings 13 a of the black mask 13. Each ofthese color filters 14R, 14G and 14B has an area larger than eachopening 13 a by an appropriate length and width over the entirecircumference, and is set in such a manner that its rim portion overlapsan opening edge portion of the black mask 13. Further, a thickness ofeach of the color filters 14R, 14G and 14B is optimally set inaccordance with each of the color filters 14R, 14G and 14B in such amanner that a liquid crystal layer thickness (a cell gap) dr, dg or dbin each pixel region where each of the color filters 14R, 14G and 14B isarranged substantially matches with a value of a product of a refractiveindex anisotropy of the liquid crystal layer in accordance withtransmission light having each wavelength and the layer thickness dr, dgor db. This optimization of the liquid crystal layer thickness will bedescribed later in detail.

A common electrode 15 formed of one film type transparentelectroconductive film covers surfaces of the color filters 14R, 14G and14B of red, green and blue having different thicknesses. Furthermore, afront homogeneous alignment film 16 which restricts alignment of liquidcrystal molecules uniformly covers a surface of the common electrode 15.As shown in FIG. 1, a surface of this front homogeneous alignment film16 is subjected to aligning treatment in a direction of an arrow 16 a bya rubbing method. This aligning treatment direction 16 a is a directionwhich crosses the horizontal direction 1 h which is parallel with thelower side 1 a on a display surface forming the rectangular shape of theliquid crystal cell 1 in an upper right direction at an angle of −45°±5°(a clockwise direction is determined as a + direction).

A plurality of pixel electrodes 17 formed of a transparentelectroconductive film are set on an inner surface of the rear glassplate 12 in a matrix arrangement in accordance with the openings 13 a ofthe black mask 13. A thin film transistor 18 as an active element iselectrically connected with each pixel electrode 17. Furthermore, a rearhomogeneous alignment film 19 is uniformly provided to cover all thepixel electrodes 17, thin film transistors 18 and others. As shown inFIG. 1, this rear homogeneous alignment film 19 is subjected to aligningtreatment in a direction indicated by an arrow 19 a perpendicular to thealigning treatment direction 16 a of the front homogeneous alignmentfilm 16 by the rubbing method. This aligning treatment direction 19 a isa direction which crosses the horizontal axis 1 h of the liquid crystalcell 1 in a lower right direction at an angle of +45°±5°.

A liquid crystal layer 110 is sealed in a space formed when the frontand rear homogeneous alignment films 16 and 19 attached on therespective inner surfaces of the two glass substrates 11 and 12 faceeach other. The sealed liquid crystal layer 110 is formed of a nematicliquid crystal having a positive dielectric anisotropy. In an initialstate where no electric field is applied, respective liquid crystalmolecules in the vicinity of the front and rear homogeneous alignmentfilms 16 and 19 are arranged upon undergoing an alignment restrictingforce along the directions 16 a and 19 a of the aligning treatmentapplied to the front and rear horizontal alignment films 16 and 19, andthe liquid crystal molecules in the liquid crystal layer aretwist-aligned between the two glass substrates 11 and 12.

That is, the respective liquid crystal molecules in the sealed liquidcrystal layer 110 are arranged in a twisted state at an angle of 90°±5°in a clockwise direction indicated by an arrow 21 from the surface ofthe rear homogeneous alignment film 19 toward the surface of the fronthomogeneous alignment film 16. Therefore, there exists a visual angledirection along which the best contrast can be obtained in this liquidcrystal display device in a direction which is rotated clockwise fromthe aligning treatment direction 19 a of the rear homogeneous alignmentfilm 19 at an angle of 45° and indicated by an outline arrow 20 (adirection of an intermediate angle in a twist angle range), i.e., adownward direction in the figure which is indicated by this outlinearrow direction 20.

The liquid crystal layer 110 in which the liquid crystal molecules aretwist-aligned as described above has wavelength dependence that therefractive index anisotropy varies depending on a wavelength of lighttransmitted therethrough. Therefore, in order to perform color displaywith high color reproducibility, a liquid crystal layer thickness whichdiffers in accordance with a pixel of each color is set in such a mannerthat a birefringence effect of substantially λ/2 is given to each ofred, green and blue wavelength lights transmitted through the liquidcrystal layer 110.

That is, in the liquid crystal cell 1 according to this embodiment, alayer thickness dr, dg or db for each pixel of red, green or blue is setto a value which offsets the wavelength dependence of a refractive indexanisotropy Δn with respect to each wavelength light.

That is, ratios of a refractive index anisotropy Δnb with respect toblue wavelength light, a refractive index anisotropy Δng with respect togreen wavelength light and a refractive index anisotropy Δnr withrespect to red wavelength light are as follows:

Δnb/Δng=1.04±0.03

Δnr/Δng=0.96±0.03

In accordance with the above-described expression, as shown in FIG. 2, afilm thickness of each of the color filters 14R, 14G and 14B is set insuch a manner that the liquid crystal layer thickness dr of a pixelhaving the red color filter 14R arranged therein becomes 5.5 μm, theliquid crystal layer thickness dg of a pixel having the green colorfilter 14G arranged therein becomes 5.0 μm and the liquid crystal layerthickness db of a pixel having the blue color filter 14B arrangedtherein becomes 4.8 μm.

A front polarizing plate 2 is set on an outer surface of the front glasssubstrate 11 of the liquid crystal cell 1. As shown in FIG. 1, thisfront polarizing plate 2 is set in such a manner that its transmissionaxis 2 a is placed in parallel with the horizontal axis 1 h of thedisplay surface as seen from the observation side. Therefore, thetransmission axis 2 a crosses the direction 16 a of the aligningtreatment applied to the front homogeneous alignment film 16 of theliquid crystal cell 1 at an angle of +45°±5°.

Furthermore, a rear polarizing plate 3 is set on an outer surface of therear glass substrate 12 of the liquid crystal cell 1. This rearpolarizing plate 3 is set in such a manner that its transmission axis 3a becomes perpendicular to the transmission axis 2 a of the frontpolarizing plate 2, i.e., parallel with a vertical direction of thedisplay surface (a direction perpendicular to the horizontal axis 1 h ofthe liquid crystal display device as seen from the observation side,which will be referred to as a vertical axis direction hereinafter).Therefore, the transmission axis 3 a crosses the direction 16 a of thealigning treatment applied to the front homogeneous alignment film 16 ofthe liquid crystal cell 1 at an angle of −45°±5°.

That is, the front polarizing plate 2 is arranged in such a manner thatits transmission axis 2 a faces a direction perpendicular to a directionof an intermediate angle (a direction indicated by the outline arrow 20)in a twist angle range in which the liquid crystal molecules in theliquid crystal layer are twist-aligned from the front homogeneousalignment film 16 toward the rear homogeneous alignment film 19 and thatan absorption axis 2 b perpendicular to the transmission axis 2 asubstantially matches with the direction of the intermediate angle.Moreover, the rear polarizing plate 3 is arranged in such a manner thatits transmission axis 3 a faces a direction substantially parallel withthe direction of the intermediate angle (the direction indicated by theoutline arrow 20) in the twist angle range in which the liquid crystalmolecules in the liquid crystal layer are twist-aligned from the fronthomogeneous alignment film 16 toward the rear homogeneous alignment film19 and that an absorption axis 3 b perpendicular to the transmissionaxis 3 a becomes substantially perpendicular to the direction of theintermediate angle and substantially perpendicular to the absorptionaxis 2 b of the front polarizing plate 2.

That is, the front polarizing plate 2 is arranged in such a manner thatits transmission axis 2 a or absorption axis 2 b matches with thedirection indicated by the arrow 20 rotated from one of the aligningtreatment directions 16 a and 19 a of the front and rear aligning films16 and 19 toward the other one at an angle (45° which is substantially ½of an angle formed between the aligning treatment direction 16 a of thefront aligning film 16 and the aligning treatment direction 19 a of therear aligning film 19.

Functions and effects of the thus configured liquid crystal displaydevice will now be described with reference to schematic explanatoryfigures of FIGS. 3 and 4. Here, FIGS. 3A and 3B show an initialalignment state of the liquid crystal molecules when no electric fieldis applied to the liquid crystal layer. FIG. 3A is a plan view, and FIG.3B is a cross-sectional view showing an alignment state of the liquidcrystal molecules between the substrates. Moreover, FIGS. 4A and 4B showa state in which a sufficiently large electric field is applied to theliquid crystal layer to rise the liquid crystal molecules. FIG. 4A is aplan view, and FIG. 4B is a cross-sectional view showing an alignmentstate of the liquid crystal molecules between the substrates.

In the initial alignment state depicted in FIGS. 3A and 3B, each liquidcrystal molecule 110 a in the vicinity of the front and rear aligningfilms 16 and 19 undergoes an alignment restricting force of thecorresponding homogeneous alignment films 16 and 19 and is aligned in anattitude that its long axis direction is parallel with each of thealigning treatment directions 16 a and 19 a and an end portion on thedownstream side of each of the aligning treatment directions 16 a and 19a is lifted at a pre-tilt angle θ. Each intermediate liquid crystalmolecule 110 b in the liquid crystal layer 110 is twist-alignedcontinuously with alignment of each liquid crystal molecule 110 a in thevicinity of each of the homogeneous alignment films 16 and 19 betweenthe two substrates. That is, the liquid crystal molecules 110 a and 110b are in twist-aligned in a range of substantially 90° extendingclockwise in a direction of an arrow 21 from the rear homogeneousalignment film 19 side toward the front homogeneous alignment film 16side. The liquid crystal layer 110 in which the liquid crystal molecules110 a and 110 b are twist-aligned in the range of 90 degrees is set tohave birefringence which generates a retardation which is ½ of awavelength λ, of transmitted light. Therefore, linear polarized lighttransmitted through this liquid crystal layer 110 exits as linearpolarized light having a polarization plane optically rotated at 90°.

In this liquid crystal display device, as shown in FIG. 1, since thetransmission axis 3 a of the rear polarizing plate 3 is perpendicular tothe transmission axis 2 a of the front polarizing plate 2, therespective absorption axes 3 b and 2 b are also arranged to beperpendicular to each other. Therefore, illumination light from abacklight 10 (see FIG. 6) is transmitted through the rear polarizingplate 3 so that its polarization plane is turned to linear polarizedlight parallel with the transmission axis 3 a and enters the liquidcrystal layer 111 in the initial alignment state. This light is providedwith a retardation of λ/2 when transmitted through this liquid crystallayer 110, and its polarization plane is optically rotated at 90°, andthis light then exits. Since the polarization plane of this exitinglinear polarized light is parallel with the transmission axis 2 a of thefront polarizing plate 2, this linear polarized light is transmittedwithout being absorbed, thereby enabling bright display.

Then, when an electric field which is sufficiently intensive tosubstantially vertically align the liquid crystal molecules 110 bpositioned in the intermediate layer of the liquid crystal layer 110with respect to the substrates is applied to the liquid crystal layer110 in order to carry out dark display, the alignment state of theliquid crystal molecules becomes as shown in FIGS. 4A and 4B.

Each liquid crystal molecule is standing-aligned in such a manner thatits long axis direction becomes parallel with a direction of the appliedelectric field, i.e., a direction vertical to the front and rear glasssubstrates 11 and 12 (see FIG. 2), and each liquid crystal molecule 110b positioned in the middle of the liquid crystal layer 110 in the layerthickness direction is substantially vertically aligned in a spiralreleasing state. On the other hand, each liquid crystal molecule 110 ain the vicinity of the front and rear homogeneous alignment films 16 and19 cannot sufficiently rise due to an anchoring effect of eachcorresponding homogeneous alignment film 16 or 19, and an intermolecularforce which releases the spiral allows each liquid crystal molecule 110a in the vicinity of each of the homogeneous alignment films 16 and 19to be aligned in such a manner that the pre-tilt angle θ remainsunchanged but the long axis direction faces a direction of anintermediate angle of the twist angel range of the twist alignment,i.e., an angle obtained by dividing an angle formed between the aligningtreatment direction 16 a of the front aligning film 16 and the aligningtreatment direction 19 a of the rear aligning film in two, namely, athird direction 20 rotated clockwise at 45° from the aligning treatmentdirection 19 a of the rear aligning film 19 (a direction of a verticalline of the liquid crystal display device in the figure).

Further, a rising angle of each liquid crystal molecule 110 b isincreased as distanced from each of the homogeneous alignment films 16and 19, and each liquid crystal molecule 110 b in the intermediateportion of the liquid crystal layer 110 is aligned in a substantiallyvertically rising state. As shown in FIG. 4A, in regard to a standingalignment state at the time of application of the electric field (at thetime of on), the respective liquid crystal molecules are aligned in astate where their long axis directions are generally aligned in thethird direction 20.

In this liquid crystal display device, as shown in FIG. 1, since therear polarizing plate 3 is arranged in such a manner that itstransmission axis 3 a is parallel with the third direction 20 in theliquid crystal cell 1, a retardation is not substantially given whenlinear polarized light transmitted through the rear polarizing plate 3is transmitted through the liquid crystal layer 110, and this lightexits as the substantial linear polarized light without change. Since adirection of the polarization plane of this exiting linear polarizedlight is a direction parallel with the absorption axis 2 b of the frontpolarizing plate 2, the front polarizing plate 2 assuredly performsabsorption, thereby obtaining excellent dark display.

FIG. 5 is a graph showing a change in transmission factor in accordancewith each wavelength light with respect to an applied voltage of thisliquid crystal display device, wherein a vertical axis representing atransmission factor is a logarithmic scale. As shown in FIG. 13 as acomparative example, in a conventional TN type liquid crystal displaydevice, a liquid crystal layer is arranged between a pair of substratesfacing each other, and front and rear polarizing plates 132 and 133 arearranged on a liquid crystal cell 131 in such a manner that theirrespective transmission axes 132 a and 133 a are aligned in the samedirections as aligning treatment directions 131 a and 131 b ofcorresponding homogeneous alignment films. In the liquid crystal cell131, the aligning treatment direction 131 a of the aligning film formedon the front substrate is set to −45° with respect to a horizontal line131 h of the liquid crystal display device, and the aligning treatmentdirection 131 b of the aligning film formed on the rear substrate is setto 45° with respect to the horizontal line 131 h. Transmission factorcharacteristics of green wavelength light obtained by this conventionalTN type liquid crystal display device are indicated by a two-dots dashline in FIG. 5.

As apparent from FIG. 5, in the liquid crystal display device accordingto this embodiment of the present invention, a transmission factor ofthe green wavelength light at the time of application of the maximumelectric field (at the time of on) where an applied voltage is 4.5 V is0.02% which is reduced to approximately 1/10 of 0.2% which is atransmission factor in the conventional example in which the sameapplied voltage is used, thereby obtaining a low cost of a black level.Consequently contrast is increased approximately tenfold.

Furthermore, in the conventional TN type liquid crystal display device,tone reversal in an intermediate tone occurs in a direction matchingwith a long axis direction of each liquid crystal molecule. However, inthe liquid crystal display device according to the embodiment of thepresent invention, since the transmission axis 3 a of the rearpolarizing plate 3 matches with the third direction 20 as describedabove, occurrence of tone reversal in the intermediate tone along thethird direction is suppressed.

As described above, in the liquid crystal display device according tothis embodiment, the front polarizing plate 2 and the rear polarizingplate 3 are respectively arranged on front and rear sides with theliquid crystal cell 1 in which the liquid crystal molecules aretwist-aligned at the angle of 90° therebetween in such a manner thattheir respective transmission axes 2 a and 3 a become perpendicular toeach other, and the transmission axis 3 a of the rear polarizing plate 3to which light from the backlight enters is arranged to match with thethird direction which is a direction of the intermediate angle in theangle range in which the liquid crystal molecules are twist-aligned.Therefore, at the time of on where an electric field is sufficientlyapplied, the third direction along which the liquid crystal molecules inthe vicinity of the aligning films are arranged becomes substantiallyparallel with the optical axis constituted of the absorption axis or thetransmission axis of the polarizing plate. Therefore, excellent darkdisplay with a sufficiently low transmission factor can be obtained,thereby improving contrast of display.

Moreover, Δn·d for each pixel in which each of the color filters 14R,14G and 14B of red, green and blue is provided is calculated based on anexpression (√3·λ/2) representing a value of retardation required torotate the polarization plane of transmitted light at 90° whileconsidering an twist effect caused by twist alignment of the liquidcrystal molecules. This value is appropriately set within a range of 380nm to 480 nm in accordance with each pixel corresponding to each colorfilter, thereby providing a multigap structure having each liquidcrystal layer thickness. Therefore, excellent dark display with asufficiently low transmission factor and high contrast can be obtainedwith respect to light of wavelength of all colors. As a result, it ispossible to acquire a white color having a good chromaticity andhigh-grade color display with excellent color reproducibility based onthis white color.

In this embodiment, the rear polarizing plate 3 may be arranged in sucha manner that its absorption axis 3 b becomes parallel with the thirddirection 20. In this case, the front polarizing plate 2 is arranged insuch a manner that its absorption axis 2 b crosses the aligningtreatment direction 16 a at an angle of 45°±5°. Even if such an opticalaxis arrangement configuration is adopted, the above-described desirableeffect can be likewise demonstrated.

Second Embodiment

A second embodiment according to the present invention will now bedescribed with reference to FIGS. 6 and 7. In this embodiment, likereference numerals denote constituent parts equal to those in the firstembodiment, thereby eliminating their explanation.

A liquid crystal display device according to this embodiment has aconfiguration in which a front viewing angle compensating film 4 is setbetween a liquid crystal cell 1 and a front polarizing plate 2 and arear viewing angle compensating film 5 is set between the liquid crystalcell 1 and a rear polarizing plate 3 in addition to the configuration ofthe liquid crystal display device according to the first embodiment. Amultigap structure of the liquid crystal cell 1 is the same as that inthe first embodiment, and Δn·d of each of red, green and blue pixels isappropriate set in a range of 380 nm to 480 nm.

As shown in FIG. 7, the viewing angle compensating films 4 and 5 areobtained by forming aligning films 42 and 52 on one surface oftransparent film substrates 41 and 51 and superimposing discotic liquidcrystal layer 43 and 53 on surfaces of these aligning films 42 and 52.In each of the discotic liquid crystal layers 43 and 53, discotic liquidcrystal molecules 43 a and 53 a each having a discoid shape are arrangedin a state where they are inclined in one direction while continuouslychanging individual angles with molecular axes 43 b and 43 b vertical toa disc surface of each liquid crystal molecule being aligned in apredetermined direction. A direction of each of molecular axes 43 b and53 b is parallel with a direction of aligning treatment applied to eachof the aligning films 42 and 52. The discotic liquid crystal molecules43 a and 53 a which are in close proximity to the aligning films 42 and52 are aligned in such a manner that their disc surfaces becomesubstantially parallel with the film substrates 41 and 51, and aninclination angle, i.e., a tilt angle of a molecular disc surface ofeach of the discotic liquid crystal molecules 43 a and 53 a apart fromthe surfaces of the aligning films 42 and 52 with respect to each of thefilm substrates 41 and 51 is increased as distanced from the respectivealigning films. As a result, the discotic liquid crystal layers 43 and53 develop a negative optical anisotropy in which an optical axis alongwhich a refractive index becomes minimum (which will be referred to asan alignment axis hereinafter) is provided in a direction along whichthe inclination angles of the molecular axes 43 b and 53 b of therespective discotic liquid crystal molecules 43 a and 53 a are averaged.

In this embodiment, as shown in FIG. 6, the viewing angle compensatingfilms 4 and 5 are set on front and rear sides with the liquid crystalcell 1 therebetween in such manner that the respective alignment axes 4a and 5 a become parallel with a third direction 20 of the liquidcrystal cell 1 and opposite to each other. That is, a direction of thealignment axis 4 a of the front viewing angle compensating film 4matches with an upper direction in a vertical direction of the liquidcrystal display device, and a direction of the alignment axis 5 a of therear viewing angle compensating film 5 matches with a lower direction ofthe same.

In the thus configured liquid crystal display device according to thisembodiment, as shown in FIG. 8, contrast in a lateral viewing angledirection of the liquid crystal display device is suddenly reduced asthe viewing angle is inclined. That is, comparing with a viewing angleat which contrast is not greater than 10, a viewing angle on both rightand left sides is not smaller than 45° in the liquid crystal displaydevice having the conventional configuration shown in FIG. 13, whereas aviewing angle on both right and left sides is very small as 15° or abovein the liquid crystal display device according to this embodiment. Thisis much smaller than approximately 37° which is a viewing angle of theliquid crystal display device according to the first embodiment. Inregard to contrast in a front direction, high contrast equivalent tothat of the liquid crystal display device according to the firstembodiment is obtained.

Therefore, according to the liquid crystal display device of the secondembodiment, since a viewing angle in a lateral viewing angle directionis considerably narrowed, it is possible to obtain a useful effect ofeffectively preventing peep by people other than an observer as well asa color reproducibility acquired by the liquid crystal display deviceaccording to the first embodiment.

The directions of the respective alignment axes 4 a and 5 a of theviewing angle compensating films 4 and 5 may be reversed from theabove-described directions. That is, even if the direction of thealignment axis 4 a of the viewing angle compensating film 4 isdetermined as the upper direction and the direction of the alignmentaxis 5 a of the viewing angle compensating film 5 is determined as thelower direction, the obtained effect remains unchanged.

Third Embodiment

A liquid crystal display device according to a third embodiment has amultigap structure of a liquid crystal cell 1 in the liquid crystaldisplay device according to the second embodiment, but Δn·d of each ofred, green and blue pixels is appropriately set in a range of 450 nm to550 nm and arrangement directions of alignment axes 6 a and 7 a ofviewing angle compensating films 6 and 7 are changed.

That is, as shown in FIG. 9, the front viewing angle compensating film 6set between a liquid crystal cell 1 and a front polarizing plate 2 isarranged in such a manner that an alignment axis 6 a of discotic liquidcrystal molecules is placed in parallel with a direction 16 a ofaligning treatment applied to a front homogeneous alignment film of theliquid crystal cell 1 (a direction of −45° with respect to a horizontalaxis 1 h of the liquid crystal display device), and a rear viewing anglecompensating film 7 set between the liquid crystal cell 1 and a rearpolarizing plate 3 is arranged in such a manner that an alignment axis 7a of discotic liquid crystal molecules is positioned in parallel with adirection 19 a of aligning treatment applied to a rear homogeneousalignment film of the liquid crystal cell 1 (a direction of +45° withrespect to the horizontal axis 1 h of the liquid crystal displaydevice).

According to the thus configured liquid crystal display device accordingto the third embodiment, retardation which remains in the liquid crystallayer 110 at the time of on due to an anchoring effect is effectivelycompensated by the front and rear viewing angle compensating films 6 and7 arranged as described above. Therefore, as shown in FIG. 10, a viewingangle in a lateral direction (a horizontal direction of the liquidcrystal display device) can be greatly improved as compared with theliquid crystal display device according to the second embodiment.

That is, as apparent from FIG. 10, the liquid crystal display deviceaccording to the third embodiment has contrast of approximately 40 orabove which is assured in a wide range of both right and left fiendangles of 80°, and also has considerably wide viewing anglecharacteristics as compared with the liquid crystal display devicehaving the conventional configuration shown in FIG. 13.

As described above, in the liquid crystal display device according tothe third embodiment, the directions of the respective alignment axes 6a and 7 a of the viewing angle compensating films 6 and 7 including thepair of discotic liquid crystal layers arranged on both the front andrear sides with the liquid crystal cell 1 therebetween are set inparallel with the aligning treatment directions 16 a and 19 a of thecorresponding homogeneous alignment films 16 and 19. As a result, theresidual retardation of the liquid crystal cell 1 at the time of on iseffectively compensated, and the viewing angle at least in the lateraldirection in the display screen is improved. As a result, according tothe liquid crystal display device according to the third embodiment, itis possible to obtain a color display quality with high colorreproducibility by the liquid crystal display device according to thefirst embodiment as well as the excellent viewing angle characteristicssufficiently wide in the lateral direction.

The directions of the respective alignment axes 6 a and 7 a of theviewing angle compensating films 6 and 7 may be reversed from theabove-described directions. That is, even if the direction of thealignment axis 6 a of the front viewing angle compensating film 6 is setto a direction of +135° with respect to the lateral direction 1 h andthe direction of the alignment axis 7 a of the rear viewing anglecompensating film 7 is set to a direction of −135° with respect to thelateral direction 1 h, the obtained effect remains unchanged.

Fourth Embodiment

A liquid crystal display device according to a fourth embodiment has themultigap structure of the liquid crystal cell 1 in the liquid crystaldisplay device according to the third embodiment, but a value of Δn·d ofeach of red, green and blue pixels is appropriately set in a range of350 nm to 450 nm, and a front retardation plate 8 is arranged between afront viewing angle compensating film 6 and a front polarizing plate 2whilst a rear retardation plate 9 is arranged between a rear viewingangle compensating film 7 and a rear polarizing plate 3 as shown in FIG.11.

These front and rear retardation plates 8 and 9 have a product Δn·d of arefractive index anisotropy Δn and a thickness d being appropriately setwithin a range of 15 nm to 55 nm, and respectively include phasedelaying axes 8 a and 9 a. Further, the front retardation plate 8 is setin such a manner that its phase delaying axis 8 a becomes parallel witha direction of an alignment axis 6 a of the superimposed front viewingangle compensating film 6, and the rear retardation plate 9 is set insuch a manner that its phase delaying axis 9 a becomes parallel with adirection of an alignment axis 7 a of the superimposed rear viewingangle compensating film 7.

According to the thus configured liquid crystal display device accordingto the fourth embodiment, a retardation compensating effect by each ofthe front and rear viewing angle compensating films 6 and 7 is furtherimproved by each of the front and rear retardation plates 8 and 9superimposed with their optical axes being matched, and residualretardation at the time of on is compensated. Therefore, as shown inFIG. 12, viewing angle characteristics in a lateral direction (adirection of a horizontal axis) is further improved as compared with theliquid crystal display device according to the third embodiment.

That is, as apparent from FIG. 12, contrast which is approximately 50 orabove is assured in a wide range of both right and left viewing anglesof 80°, which is higher than the contrast of 40 or above in the samerange of the liquid crystal display device according to the thirdembodiment. Therefore, the contrast is uniformly improved in the entireviewing angle range excluding the vicinity of a front direction.

As described above, in the liquid crystal display device according tothe fourth embodiment, the viewing angle compensating films 6 and 7including the discotic liquid crystal layers and the respectiveretardation plates 8 and 9 are superimposed on both the front and rearsides with the liquid crystal cell 1 therebetween in such a manner thatthe respective optical axes are aligned in parallel with the aligningtreatment directions 16 a and 19 a of the corresponding homogeneousalignment films 16 and 19. Therefore, residual retardation in the liquidcrystal cell 1 at the time of on can be effectively compensated, and theviewing angle at least in the lateral direction in the display screencan be further improved. As a result, according to the liquid crystaldisplay device of the fourth embodiment, it is possible to obtain acolor display quality having excellent color reproducibility realized bythe liquid crystal display device according to the first embodiment aswell as excellent viewing angle characteristics with the viewing anglefurther widened in at least the horizontal axis direction.

In case of the fourth embodiment, like the liquid crystal display deviceaccording to the third embodiment, directions of the respectivealignment axes 6 a and 7 a of the viewing angle compensating films 6 and7 may be reversed from the above-described directions. The effectobtained in this case is the same as the above-described effect.

The present invention is not restricted to the first to fourthembodiments. For example, in the first to fourth embodiments, thearrangement of the transmission axis 3 a of the rear polarizing plate 3matches with the direction of the intermediate angle in the twistalignment angle range of the liquid crystal molecules in the liquidcrystal cell 1. However, it is good enough to match the transmissionaxis 3 a of this rear polarizing plate 3 with the third direction alongwhich the liquid crystal molecules in the vicinity of the homogeneousalignment film on a corresponding side at the time of on where anelectric field is sufficiently applied to the liquid crystal layer 110.For example, even if the third direction is a direction of an anglewhich is approximately ⅓ of the range of the twist alignment angle ofthe liquid crystal molecules, matching the transmission axis 3 a of therear polarizing plate 3 with this direction can suffice.

Furthermore, the present invention is not restricted to the color liquidcrystal display device in which the color filters are provided, and itcan be effectively applied to a liquid crystal display device whichperforms monochrome display.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventionconcept as defined by the appended claims and their equivalents.

1. A liquid crystal display device comprising: first and secondpolarizing plates which are arranged such that respective transmissionaxes thereof are perpendicular to each other as seen from an observationside of the liquid crystal display device; a liquid crystal cell whichis arranged between the first and second polarizing plates, and whichhas a rectangular shape as seen from the observation side; and abacklight which is provided on a side of the polarizing plate which isnot positioned on the observation side, opposite from the liquid crystalcell; wherein the liquid crystal cell includes: a first substrate havingat least one first electrode on one side; a second substrate having atleast one second electrode; and a liquid crystal layer which includesliquid crystal molecules, which is provided between the first and secondelectrodes, and which is in a homogeneous state when an electric fieldis not applied between the first and second electrodes, wherein theliquid crystal layer is set such that, when in the homogeneous state, asseen from the observation side, the liquid crystal molecules aretwist-aligned from a first molecular aligning direction on a side of theliquid crystal layer adjacent to the second substrate toward a secondmolecular aligning direction on a side of the liquid crystal layeradjacent to the second substrate, wherein a line substantially bisectinga twist angle defined between the first and second molecular aligningdirections is parallel or perpendicular to each peripheral side of theliquid crystal cell and is parallel or perpendicular to each of thetransmission axes of the first and second polarizing plates, wherein theliquid crystal display device further comprises: a first viewing anglecompensating film which is arranged between the first polarizing plateand the liquid crystal cell, and which has a first layer of discoticliquid crystal molecules which have a negative optical anisotropy, andof which inclination angles are continuously changed in a thicknessdirection of the first layer, an optical axis of the first layer beingparallel to an aligning direction of the discotic liquid crystalmolecules on a side of the first substrate, as seen from the observationside of the liquid crystal display device; a second viewing anglecompensating film which is arranged between the second polarizing plateand the liquid crystal cell, and which has a second layer of discoticliquid crystal molecules which have a negative optical anisotropy, andof which inclination angles are continuously changed in a thicknessdirection of the second layer, an optical axis of the second layer beingparallel to an aligning direction of the discotic liquid crystalmolecules on a side of the second substrate, as seen from theobservation side of the liquid crystal display device; a firstretardation plate arranged between the first polarizing film and thefirst viewing angle compensating film in such a manner that an opticalaxis of one of a phase advancing axis and a phase delaying axis issubstantially parallel with the optical axis of the first viewing anglecompensating film; and a second retardation plate arranged between thesecond polarizing film and the second viewing angle compensating film insuch a manner that an optical axis of one of a phase advancing axis anda phase delaying axis is substantially parallel with the optical axis ofthe second viewing angle compensating film.
 2. The liquid crystaldisplay device according to claim 1, wherein the twist angle of theliquid crystal molecules is 90 degrees.
 3. The liquid crystal displaydevice according to claim 2, wherein a product Δn·d is set to fallwithin a range of 350 nm to 450 nm, wherein Δn is a refractive indexanisotropy of a liquid crystal of the liquid crystal layer with respectto light transmitted therethrough, and d is a layer thickness of theliquid crystal layer through which the light is transmitted, and whereinretardations of the first and second retardation plates are respectivelyset to fall within a range of 15 nm to 55 nm.
 4. The liquid crystaldisplay device according to claim 1, wherein the liquid crystal cellincludes a plurality of color filters arranged in accordance withrespective pixels, and a thickness of the liquid crystal layer is set todifferent values in accordance with the respective pixels correspondingto the color filters having the different colors.
 5. The liquid crystaldisplay device according to claim 1, wherein each of the first andsecond viewing angle compensating films further includes a transparentfilm substrate and an aligning film formed on one surface of the filmsubstrate on which the layer of discotic liquid crystal molecules isprovided.
 6. The liquid crystal display device according to claim 5,wherein the discotic liquid crystal molecules have a disc shape withopposite flat surfaces, wherein the discotic liquid crystal moleculespositioned adjacent to the aligning film are aligned such that the flatsurfaces are parallel to the film substrate, and the discotic liquidcrystal molecules positioned apart from the aligning film are alignedsuch that the flat surfaces are inclined with the film substrate at theinclination angles, and wherein the inclination angles are increased asthe discotic liquid crystal molecules distance from the aligning film.7. The liquid crystal display device according to claim 6, wherein thenegative optical anisotropy of the discotic liquid crystal molecules hassuch a state that the optical axis along which a refractive indexbecomes minimum is provided in a direction along which the inclinationangles are averaged.